Various processes and systems have been proposed for recovering water from sewer mains. However, in view of the high levels of organic matter in sewage, such systems have always previously included a settlement process, more usually as part of, or in conjunction with, some form of biological digestion process.
Some of these prior art systems have included an anaerobic processing stage which generally requires the slurry to be stored in a holding tank or chamber without oxygenation. Similarly, the preferred aerobic treatment often used in these systems is the activated sludge process which again necessitates storing the slurry in some form of tank arrangement. Air is then injected into the slurry by various means to promote biological digestion by aerobic bacteria.
After the biological treatment, the resulting effluent of the prior art is further treated in various known manners including processes such as chemical coagulation and flocculation, multi-media sand filtration, and chlorination, etc.
Systems of the kind referred to above have several disadvantages. Firstly, the inclusion of any form of settlement or holding tank will not only potentially increase the processing time, it immediately makes the system bulky and cumbersome, thereby placing restrictions on where and how the treatment plant is located. Furthermore, odour control problems are often encountered when using such systems.
Where long residence time biological treatment stages are included, there is the additional disadvantage of needing to keep the system operating at all times so as to preserve the growth of bacteria required for the various biological processes to work effectively. With activated sludge systems, this means that the expense associated with injecting air and operating these systems must still be incurred even when additional water is not required, such as during periods of heavy rain.
It is an object of the present invention to provide a process and apparatus for recovering water from raw sewage extracted from a sewer, that overcomes or at least ameliorates one or more of the above discussed disadvantages of the prior art.